*{
    box-sizing: border-box;
}
html,
body{
    width: 100%;
    height: 100%;
    font-size: 20px;
    margin: 0;
    padding: 0;
    
}
#app{
    display: block;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: #f5f5f5;
}